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Identification of major tyrosine-phosphorylated proteins in Csk-deficient cells
Abstract:
Csk is a non-receptor protein-tyrosine kinase that acts as a negative regulator of Src family tyrosine kinases. Csk-deficient mouse embryos exhibited developmental defects including inability to turn and impaired formation of neural tube. In these embryos, an accumulation of tyrosine phosphorylated proteins was observed as a consequence of constitutive activation of Src family kinases. In order to identify those tyrosine phosphorylated proteins, we established a Csk-deficient cell line from embryos lacking both Csk and the anti-oncogene product p53. On surveying several proteins known as Src substrates, we found that phosphorylation level of p80/85 (cortactin) was markedly elevated in the Csk-deficient cells. Enhancement of cortactin phosphorylation was also seen in Csk-deficient embryos. Furthermore, immunoprecipitated Src was able to directly phosphorylate cortactin in vitro. Thus, we suggest that cortactin is a good substrate of activated Src family kinases in vivo and may play important roles in signaling pathways mediated by Src family kinases.
Insights
Csk deficiency leads to developmental defects due to activated Src kinases. Cortactin (p80/85) is identified as a key substrate, with elevated phosphorylation observed in Csk-deficient cells and embryos.
Area of Science:
- Cellular Biology
- Molecular Biology
- Developmental Biology
Background:
- Csk (a non-receptor protein-tyrosine kinase) negatively regulates Src family kinases.
- Csk deficiency in mice causes developmental defects like neural tube formation impairment.
- Constitutive Src family kinase activation leads to increased tyrosine phosphorylation in Csk-deficient embryos.
Purpose of the Study:
- To identify tyrosine phosphorylated proteins accumulating in Csk-deficient cells.
- To investigate the role of cortactin as a potential Src substrate in vivo.
Main Methods:
- Established a Csk-deficient cell line from double-deficient embryos (Csk-/- and p53-/-).
- Analyzed phosphorylation levels of known Src substrates in Csk-deficient cells and embryos.
- Performed in vitro kinase assays using immunoprecipitated Src and cortactin.
Main Results:
- Cortactin (p80/85) phosphorylation was significantly elevated in Csk-deficient cells.
- Increased cortactin phosphorylation was also observed in Csk-deficient embryos.
- Src directly phosphorylated cortactin in vitro, confirming it as a substrate.
Conclusions:
- Cortactin is a direct and significant substrate of activated Src family kinases in vivo.
- Elevated cortactin phosphorylation in Csk deficiency suggests its involvement in Src-mediated signaling pathways.
- Cortactin may play crucial roles in developmental processes regulated by Src family kinases.